1. Field of the Invention
The present invention relates to an electronic system for diverting electric current to an electrical load.
2. Description of the Related Art
Catalytic converters are widely employed in automobiles to reduce emissions from automobile engines. One limitation of typical catalytic converters is that they perform optimally only when the catalysts within them are warm. Typically, several minutes of engine operation are needed for an engine's exhaust gases to warm the catalyst in a catalytic converter. As a result, catalysts will operate with reduced efficiency for those several minutes. With the ever-increasing requirements for lower automotive emissions, such reduced efficiency can be a detriment.
A catalyst which can dramatically reduce the period of operation with such reduced efficiency is an electrically-heated catalyst (EHC). In addition to their ability to be heated by exhaust gases, EHCs can be heated by passing electric current through them. As a result, EHCs can be warm much sooner than traditional catalysts.
One drawback of EHCs is that, although they heat quickly, they require a great deal of electrical current. The amount of current can be over 100 amperes and can thus approach the entire current-generating capacity of many automobile alternators. An EHC in combination with other electrical loads on a vehicle can easily outstrip the current-generating capacity of an alternator. Those other loads include high-current loads such as a 12-volt battery which is charged by the alternator, headlights and a rear window defroster grid.
Because of the excessive electric current demands which can be placed on an alternator by an EHC and other loads, a system which diverts essentially all of an alternator's current to the EHC for the time needed to heat the EHC will be advantageous. While the diversion is occurring, other loads on the vehicle would be powered from energy stored in the 12-volt battery. After the EHC is warm, the system would stop diverting current to the EHC. Current from the alternator would then flow instead to the 12-volt battery and the other electrical loads on the vehicle.
A means employed in the prior art to divert current to an intermittent high-current load (specifically an electrically-heated windshield) is a double-throw electromechanical relay. In one state, the relay is switched such that current can flow from the alternator to the intermittent load. In the other state, the relay is switched such that current can flow to the other loads on the vehicle. Although a relay as a diverter generally serves the intended purpose, its abrupt switching of the high currents involved can cause problems. Most significantly, the durability of the relay is compromised by the abrupt switching of the high currents.
Therefore, a system which can divert current to an intermittent high-current load without the use of an electromechanical relay will provide advantages over the prior art.